Phenoxybenzoic acid derivatives containing a sulfonamide group are known to have herbicidal properties. Some of these derivatives are described in European Patent Application Nos. 3,416 and 23,392, Japanese Patent Application No. 82/106,654 and U.S. Pat. No. 4,285,723 These references describe methods of making certain compounds falling within formula (I) above, by reacting, at a temperature between 25.degree. and 140.degree. C., an intermediate acid halide of the formula: ##STR3## in which X is chlorine, bromine or iodine and A, Z, Z.sup.1, D, E and W have the meanings already indicated, with a sulphonamide of the formula: EQU R.sup.3 SO.sub.2 NH.sub.2 (III)
in which R.sup.3 has the meaning already indicated, generally in the presence of an acid acceptor, in particular a tertiary amine such as N,N-dimethylaniline or pyridine, an alkali metal carbonate such as anhydrous potassium carbonate or an alkali metal fluoride such as caesium fluoride.
The compounds of the formula (I) can then be alkylated in any manner known to those of ordinary skill in the art. This may be accomplished by a reaction with a diazoalkane having one to four carbon atoms, so as to give the corresponding products substituted on the nitrogen atom of the sulphonamide group by an alkyl group having one to four carbon atoms; the hydrogen atom on this same nitrogen atom can also be replaced by alkali metal atoms for example, sodium, by reacting with basic alkali metal reagents.
It has been found that this known process for condensing the products of formulae (II) and (III) has various disadvantages, in particular, mediocre yields. It is considered that, in general, this is due to the presence of the acid acceptor, which lowers the yield by promoting a diacylation reaction. Furthermore, the use of an acid acceptor makes the isolation and purification of the final products more difficult and more expensive.
Another disadvantage of the known process is that it requires an additional reaction step to obtain the acid halide of the formula (II) from the corresponding acid of the formula. ##STR4##
One object of the invention is to overcome the disadvantages of the known processes.
Another object of the invention is to make it possible to prepare compounds of the formula (I) from technical-grade or industrial-grade reactants of the formula (IV).
In practice, the latter problem is all the more important because this type of acid is capable of containing a considerable number of impurities as a result of the number and nature of the reactions used to manufacture it. Thus, by way of non-limiting example, acifluorfen, having the formula: ##STR5## can be prepared by coupling an alkali metal meta-cresolate with a 3,4-dihalogenotrifluoromethylbenzene, followed by oxidation of the CH.sub.3 group to a carboxylic acid group and then nitration. During a reaction sequence of this type, the number of isomers and other undesirable compounds progressively increases and, in acifluorfen of ordinary grade, it is common to detect a large number of acids, more particularly: 2-nitro-3-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-benzoic acid in an amount which can easily reach 16% by weight, 2-nitro-5-[2'-chloro-5'-(trifluoromethyl)-phenoxy]-benzoic acid and 4-nitro-5-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-benzoic acid, it easily being possible for these last two acids to be present in amounts ranging up to 3% by weight, together with a series of other acids in amounts which can also range up to 3%, this amount frequently being lower, however, e.g., less than 0.5%, such as e.g., 3-[2'-chloro-5'-(-trifluoromethyl)-phenoxy]-benzoic acid, 3-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-benzoic acid and 2,4-dinitro-5-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-benzoic acid, as well as 4-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-nitrobenzene and 2-nitro-5-[2'-chloro-4'-(trifluoromethyl)-phenoxy]-toluene.
It is, therefore, an object of this invention to provide a process for making the desired end products with high purity and high yield from compounds of formula (IV) of low purity.
It is another object of this invention to provide a process for preparing the desired end product having high purity and high yield from technical grade or industrial grade starting reactant.
It is a further object of this invention to provide a process for preparing the desired end product without using an acid acceptor.
It is a still further object of this invention to provide a process for making the desired end products in as fews steps as possible.
Other advantages will become apparent in the course of the discussion which now follows.